These gene networks offer potential targets for new medications for these conditions, according to the researchers.

Autism spectrum disorders (ASDs) can cause restricted behaviors as well as problems with children's social interaction and communication. ADHD is a disorder that affects impulsivity and attention.

In general, the symptoms and the genetics of these disorders are often different, according to study author Dr. Hakon Hakonarson, director of the Center for Applied Genomics at The Children's Hospital of Philadelphia.

"However, the common biological patterns we are finding across disease categories strongly imply that focusing on underlying molecular defects may bring us closer to devising therapies," Hakonarson said in a hospital news release.

The genome-wide association study, published online June 6 in Nature Communications, involved more than 6,700 patients with an autism spectrum disorder. These patients were compared to more than 12,500 people who did not have autism.

Researchers found three gene networks, which include a family of proteins that regulate cell signaling and neurotransmitters. Neurotransmitters are substances that help cells communicate with each other. Another gene network implicated is involved in cancer development and may help explain the reported link between autism and certain forms of cancer.

The researchers also focused on a pathway involving a family of genes that affects the neurotransmitter glutamate. They explained that glutamate plays a significant role in certain brain functions, such as memory, learning, thinking, attention and behavior. The researchers noted these are all processes that are relevant to autism.

Previous studies have shown that at least 10 percent of patients with ADHD also have changes in this pathway. Scientists have also suggested that these gene defects are linked to schizophrenia.

The study's authors are planning a clinical trial to test a drug that activates this pathway on certain ADHD patients.

"If drugs affecting this pathway prove successful in this subset of patients with ADHD, we may then test these drugs in autism patients with similar gene variants," Hakonarson explained.

The study authors noted that larger studies are needed to investigate the genetics of autism, particularly the brain's glutamate signaling pathway.

"Even though our own study was large, it captures only about 20 percent of genes causing ASDs," said Hakonarson.